Exhaust hoods are used in many situations where pollutants are generated. Examples include kitchens, laboratories, factories, and spray paint booths, as well as other examples. In a commercial kitchen environment, multiple exhaust hoods and exhaust ducts may be provided for different appliances at different locations. The load varies with the type of appliance and the way it is being used. Broilers, grills, and fryers, for example, may produce a great deal of smoke and fumes, including grease particles and moisture. Other devices such as ovens and steam tables may produce less. To provide sufficient flow to remove pollutants without removing excessive amounts of air creates a real time flow balancing problem in the commercial kitchen environment. Typical exhaust hoods and ducting systems may be ill-suited to addressing this problem in an optimum way.
A typical exhaust hood has an inlet for fumes and air that leads to an exhaust duct. Filters may be provided at the point where air and fumes enter the duct. An exhaust plenum may also connect the hood with the exhaust duct. Hoods are often long and narrow and accommodate multiple cooking units. Variations include exhaust ceilings, wide canopy hoods, and other configurations.
Prior art systems have used flow restrictions in the path of the exhaust air to balance the flow of air and fumes. Dampers or other chokes may be used to make adjustments to the flow and real time control systems have been proposed. But fouling is a persistent problem particularly in systems that handle fumes and air with water vapor and grease particles.